Sensitization of glyoxylate photoinitiators using a terphenyl compound

ABSTRACT

Glyoxylate photoinitiators are sensitized for photoinitiation by the use of at least one terphenyl sensitizer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the sensitization of glyoxylatephotoinitiators.

2. Description of the Prior Art

Glyoxylate photoinitiators are known compounds and possess theglyoxylate group (--C(O)--C(O)--O--) attached to suitable moieties whichconfer photoinitiator utility on the resulting compound. Compounds ofthis type are described in U.S. Pat. No. 4,038,164 to F. A. Via, whichis incorporated herein by reference. That patent describes compounds ofthe formula ##STR1## where R can be a straight or branched chainhydrocarbon (e.g. C₁ -C₁₀ alkyl) of from one to ten carbon atoms, aryl,aralkyl, or mono-, di-, or trisilyl and R' is an aromatic heterocycle,aryl of from 6 to 14 carbon atoms, or mono-, di- or polysubstitutedphenyl with such substituents as alkyl, alkoxy, aryloxy, alkylthio,arylthio and halogen. Preferably, R is alkyl and R' is phenyl. Acommercial product of this type is sold under the trademark VICURE-55 byStauffer Chemical Company and contains methyl phenyl glyoxylate as thephotoinitiator.

SUMMARY OF THE PRESENT INVENTION

It has now been found that terphenyl compounds can function as effectivesensitizers for the above-described glyoxylate photoinitiators.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The compositions curable by actinic radiation according to the inventioncan contain a polymerizable polymer in a reactive ethylenicallyunsaturated monomeric medium, a reactive polymer alone, a reactivemonomer alone, or any of these combined with an inert solvent.Additionally, the polymerizable composition can contain any of thepigments commonly used in photopolymerization techniques.

The procedure can be carried out by mixing a quantity of photoinitiatingcompound of the present invention with a photopolymerizable compositionand exposing the resultant mixture to actinic radiation. Alternatively,a one-component system comprising the photopolymerizable composition,the photoinitiator of the invention and, if desired, pigmentation, canbe formed.

The photoinitiating compounds of the invention are suitable in theactinic light curing of unsaturated monomeric compounds either alone oras copolymerizable constituents of unsaturated polymer/monomer systems.Such systems are composed of mixtures of conventional unsaturatedpolymers and unsaturated monomers.

Monomers which are useful in practicing the invention are acrylic,α-alkacrylic and α-chloroacrylic acid compounds such as esters, amidesand nitriles. Examples of such compounds are acrylonitrile,methacrylonitrile, methyl acrylate, ethyl acrylate, methyl methacrylate,isobutyl methacrylate, 2-ethylhexyl acrylate, methacrylamide and methylα-chloroacrylate. Also useful, although not preferred due to theirslower rates of reactivity, are vinyl and vinylidene esters, ethers andketones. Additionally, compounds having more than one terminalunsaturation can be used. Examples of these include diallyl phthalate,diallyl maleate, diallyl fumarate, triallyl cyanurate, triallylphosphate, ethylene glycol dimethylacrylate, glycerol trimethylacrylate,pentaerythritol triacrylate, pentaerythritol tetraarylate,trimethylolpropane triacrylate, methacrylic anhydride, and allyl ethersof monohydroxy or polyhydroxy compounds, such as ethylene glycol diallylether, pentaerythritol, tetraallyl ether, and the like. Nonterminallyunsaturated compounds such as diethyl fumarate can similarly be used.

The acrylic acid derivates are particularly well suited to the practiceof the invention and are consequently preferred components as monomersin monomer-containing polymerizable systems and as reactive centers inpolymerizable polymers. While monomeric styrene can be used in thepractice of the invention, it is not a preferred constituent of systemspolymerizable thereby due to its slow rate of reaction.

A preferred manner of practicing the invention is by the use ofphotopolymerizable molding and coating compositions which comprisemixtures of unsaturated polymeric compounds and monomeric compoundscopolymerizable therewith. The polymeric compounds can be conventionalpolyesters prepared from unsaturated polycarboxylic acids such as maleicacid, fumaric acid, glutaconic acid, itaconic acid, citraconic acid,mesaconic acid and the like, and polyhydric alcohols such as ethyleneglycol, diethylene glycol, glycerol, propylene glycol, 1,2-butanediol,1,4-butanediol, pentaerythritol, trimethylolpropane and the like. Thecarboxylic acid content can also contain saturated components. Theinclusion of a monobasic fatty acid content, either as such or in theform of a triglyceride or oil, in the photopolymerizable polyestercomposition to comprise an alkyd resin is also acceptable. These resinscan, in turn, be modified by silicones, epoxides, isocyanates, etc., byknown techniques.

In accordance with the present invention the glyoxylate-containingphotopolymerizable composition contains an effective amount (e.g., fromabout 0.1% to about 10%, by weight of the photopolymerizablecomposition) of a terphenyl compound to sensitize the initiator tophotopolymerization. If desired, the terphenyl compound can contain oneor more substituents on any of the phenyl rings including alkyl,alkoxyor halogen. Representative terphenyl compounds which are useful includep-terphenyl and, preferably, m-terphenyl.

Thus it is seen that the constitution of photopolymerizable compositionswhich can be used in the practice of the invention is widely variable.However, the compounds enumerated above are purely illustrative.Materials subject to polymerization by actinic radiation as well aspermissible variations and substitutions of equivalent components withinparticular types of compositions are well known to those skilled in theart.

The glyoxylate photoinitiators can be utilized in amounts ranging from0.01 to about 30% by weight based on the photopolymerizable composition.However, preferable amounts of the compounds are from about 0.5 to about20 weight percent with optimal results being achieved with amounts inthe range of from about 1.0 to about 16 weight percent.

An acceptable source of actinic light radiation is any apparatus whichemits light radiation in the approximate region of from about 2000Angstroms to about 8000 Angstroms and preferably from about 2400Angstroms to about 5400 Angstroms. One such apparatus is PPG Model QC1202, a UV processor, manufactured by PPG Industries, Inc.

The present invention is illustrated by the Examples which follow.

TEST PROCEDURE USED IN THE EXAMPLES

The induced rate of photopolymerization of a standard test solution ofacrylate/alkyd resin was measured for each of the compounds tested. Thisstandard test solution consisted of 42%, by weight, trimethylolpropanetriacrylate (TMPTA), 17% by weight, of ethylhexyl acrylate (EHA), and41%, by weight of an unsaturated long chain linseed oil alkyd resin(ACTOMER X-80 resin from Union Carbide).

The test solution was exposed to light radiation from a light source(PPG Model QC 1202) which contained two high intensity, medium pressurequartz mercury lamps, 12 inches in length, with each operating at alinear power density of about 200 watts per inch or 2400 watts per lamp.The lamps were housed in an elliptical reflector above a variable speedconveyor belt so that each lamp provided a 2-inch band of high fluxactinic radiation on the conveyor. This 2-inch exposure area wasbordered on both sides by an additional 2-inch area of medium fluxenergy for a total radiation area of 6 inches for each lamp. In thecuring data presented herein, the cure rate of the polymerizablecompositions is presented in feet-per-minute-per-lamp (ft./min./lamp).Thus, a conveyor belt speed of one foot/min. will, with a 12-inchexposure area for the two lamps, provide 60 seconds of exposure or acure rate of 0.5 ft./min./lamp. Similarly, a belt speed of 10 ft./min.will provide 6 seconds of exposure or a rate of 5.0 ft./min./lamp, whilea speed of 20.0 ft./min. will give 3 seconds exposure or a rate of 10ft./min./lamp.

The extent of curing was determined by a standard pencil hardness testwith all samples being coated on aluminum plate to a thickness of 2 milsand polymerized to achieve standard pencil hardness of from 4H to 6Hwhere this was attainable.

EXAMPLES 1-3

In the following Examples the standard test solution was used withmethyl phenyl glyoxylate being used as the photoinitiator at 4 wt.percent in all cases. The terphenyl compound was used at 1 wt. percentin all cases.

    ______________________________________                                                         Cure Rate                                                    Sensitizer       (ft/min/lamp)                                                ______________________________________                                        None used (Control)                                                                            14                                                           meta-terphenyl   20                                                           para-terphenyl   15                                                           ______________________________________                                    

The foregoing Examples should not be construed in a limiting sense sincethey merely illustrate certain embodiments of the present invention. Thescope of protection sought is set forth in the claims which follow.

What is claimed:
 1. In the photopolymerization of monomeric andpolymeric compositions of photopolymerizable substances wherein aphotoinitiator is admixed with a photopolymerizable composition and themixture exposed to actinic radiation, the improvement whereinphotopolymerization is effectively initiated by a glyoxylatephotoinitiator in the presence of a terphenyl compound sensitizer forsaid photoinitiator.
 2. The method of claim 1 wherein the photoinitiatoris of the formula ##STR2## where R is lower alkyl and R' is phenyl. 3.The method of claim 1 wherein the photoinitiator is methyl phenylglyoxylate.
 4. The method of claim 1 wherein the terphenyl compound ismeta-terphenyl.
 5. The method of claim 1 wherein the terphenyl compoundis para-terphenyl.
 6. The method of claim 1 wherein the photoinitiatoris methyl phenyl glyoxylate and the sensitizer is meta-terphenyl.
 7. Themethod of claim 6 wherein the photoinitiator is present at from about1.0 to about 16 weight percent of the photopolymerizable composition andthe sensitizer is present at from about 0.1% to about 10% by weight ofthe photopolymerizable composition.
 8. A composition photopolymerizableby actinic radiation comprising unsaturated polymerizable constituentscontaining dispersed therein an effective amount of a glyoxylatephotoinitiator and a terphenyl compound sensitizer for saidphotoinitiator.
 9. The composition of claim 8 wherein the photoinitiatoris of the formula ##STR3## where R is lower alkyl and R' is phenyl. 10.The composition of claim 8 wherein the photoinitiator is methyl phenylglyoxylate.
 11. The composition of claim 8 wherein the terphenylcompound is meta-terphenyl.
 12. The composition of claim 8 wherein theterphenyl compound is para-terphenyl.
 13. The composition of claim 11wherein the photoinitiator is methyl phenyl glyoxylate and thesensitizer is meta-terphenyl.
 14. The composition of claim 13 whereinthe photoinitiator is present at from about 1.0 to about 16 weightpercent of the photopolymerizable composition and the sensitizer ispresent at from about 0.1% to about 10% by weight of thephotopolymerizable composition.